1. Technical Field
The present disclosure relates to an industrial network apparatus and a data transmission method.
2. Related Art
In a manufacturing system or a manufacturing apparatus, generally, N industrial devices (slaves) such as servo amplifiers or I/O devices are connected to an industrial network. These industrial devices communicate with a controller (a master) that controls them in a one-to-N manner (N≧1). In this case, a real-time exchange between a command (an instruction value; output data) from the master and a response (a current value; input data) from the slave is required between the master and each slave. Therefore, the master and the slave repeat the exchange of the input data and the output data within a predetermined period (a transmission cycle) so-called communication cycle or transmission cycle.
Here, the accuracy of the transmission cycle is required in motion control systems such as machine tools or chip mounters. This is because of the following reason. In the motion control systems, multiple devices such as servo drives are simultaneously operated synchronized with the transmission cycle. Therefore, the more accurate the transmission cycle is, the more the synchronization accuracy improves, which results in the improvement of the manipulation accuracy.
By the way, in manufacturing systems or manufacturing apparatus, the maintenance or engineering of the connected equipment is carried out in addition to the highly prioritized exchange of the input and output data executed by a fixed cycle. Thus, the manufacturing system or the manufacturing apparatus is required to perform the less prioritized, irregular data transmission (hereafter, referred to as “message transmission”). When such message transmission is executed, however, the band of the exchange of the input and output data may be affected, which is likely to make it difficult to ensure the real-time property. Furthermore, the simultaneous operation of the devices is likely to be disturbed due to the expanded transmission cycle.
It is noted that the art of performing the cyclic exchange of the input and output data and the message transmission without affecting the transmission cycle is known as an FL-net (OPCN-2) disclosed in Japanese Patent Application Laid-open No. 2005-215936. In the FL-net, the connected equipment that has been qualified for a transmission by a token pass simultaneously broadcasts the input data or the output data. When there is a margin in the remaining band of the transmission cycle, the message transmission is made. This allows for the real-time communication by a fixed cycle.